1. Field of the Invention
The present invention relates to a method of frame plating and a method of forming a magnetic pole of a thin-film magnetic head through the use of the method of frame plating.
2. Description of the Related Art
Performance improvements in thin-film magnetic heads have been sought as areal recording density of hard disk drives has increased. Such thin-film magnetic heads include composite thin-film magnetic heads that have been widely used. A composite head is made of a layered structure including a write (recording) head having an induction-type electromagnetic transducer for writing and a read (reproducing) head having a magnetoresistive (MR) element for reading.
It is required to increase the track density on a magnetic recording medium in order to increase recording density among the performance characteristics of a write head. To achieve this, it is required to implement a write head of a narrow track structure wherein the track width, that is, the width of top and bottom magnetic poles sandwiching the write gap layer on a side of the air bearing surface (medium facing surface) is reduced down to microns or the order of submicron. Semiconductor process techniques are utilized to implement such a structure.
For example, frame plating is used as a method for forming the magnetic poles that define the track width. In a conventional method of frame plating, as disclosed in Published Unexamined Japanese Patent Application Sho 50-95147, an electrode film is formed on a base layer, a resist layer is formed on the electrode film, and this resist layer is patterned through a photolithography process to form a frame to be used for plating. Using this frame, plating is performed through the use of the electrode film previously formed as a seed layer. A patterned plating pattern is thereby formed.
According to the conventional method of frame plating, a resist layer is patterned using optical measures and a patterned plating layer is formed using the resulting frame, and therefore it is theoretically impossible to form a plating layer patterned more finely than a dimension determined by an optical limit. Consequently, it has been impossible, by means of frame plating, to form a magnetic pole finer than the dimension determined by an optical limit.
For example, a method of forming a finely patterned resist layer is disclosed in Published Unexamined Japanese Patent Applications Hei 6-250379, Hei 10-73927 and Hei 11-204399 as follows. Specifically, in this method, a first resist containing a material generating an acid is used to form a first patterned resist layer and this first patterned resist layer is coated with a second resist that is water-soluble and capable of entering into a crosslinking reaction in the presence of an acid, to allow the acid to be generated in the first patterned resist layer, thereby forming a crosslinking film in a portion of the second resist near the boundary that touches the first patterned resist layer, followed by peeling off the non-crosslinked portion of the second resist to form a second patterned resist layer. In the present application, this method is hereinafter called a finely patterned resist layer-forming method.
The finely patterned resist layer-forming method described above was developed for a dry step such as dry etching used in usual technologies concerning production of semiconductors as shown in Published Unexamined Japanese Patent Applications Hei 10-73927 and Hei 11-204399.
The inventor of the present invention thought of using the patterned resist layer obtained by the above-mentioned finely patterned resist layer-forming method as a frame for frame plating in order to form a plating layer patterned more finely than the dimension determined by an optical limit.
However, through an experiment the inventor found that no finely patterned plating layer was obtainable by simply using the patterned resist layer formed by the finely patterned resist layer-forming method as the frame for frame plating to form a patterned plating layer.
Here, reference is made to FIG. 23 to FIG. 33 to describe the method used in the experiment for forming the patterned plating layer, and, at the same time, the fact that no finely patterned plating layer is obtainable by this method will be explained.
In this method, as shown in FIG. 23, a base film 152 for plating is first formed using a conductive material as necessary on a layer 151 which will be a base of a plating layer to be formed.
Next, as shown in FIG. 24, a first resist containing a material generating an acid is applied and then prebaked to form a first resist layer 153.
Then, as shown in FIG. 25, the first resist layer 153 is subjected to an exposure step, a baking step in succession to the exposure step, a developing step, a washing step and a drying step in this order to form a first patterned resist layer 153A having an isolated trench. However, the aforementioned drying step may be omitted.
Thereafter, as shown in FIG. 26, a second resist that is water-soluble and capable of entering into a crosslinking reaction in the presence of an acid is applied to cover the first patterned resist layer 153A, thereby forming a second resist layer 154.
Next, as shown in FIG. 27, heat treatment for the first patterned resist layer 153A and the second resist layer 154 is carried out to generate an acid in the first patterned resist layer 153A and to diffuse the acid to the second resist layer 154. A crosslinked film 154A is thereby formed in a portion of the second resist layer 154 near the boundary that touches the first patterned resist layer 153A.
Here, the crosslinked film 154A grows only from the surface of the first patterned resist layer 153A and therefore the adhesion of the crosslinked film 154A to the base film 152 is weakened. Also, if the heat resistance of the first patterned resist layer 153A is low (low glass transition temperature), the first patterned resist layer 153A is strained when the first patterned resist layer 153A and the second resist layer 154 are heat-treated. As a result, the crosslinked film 154A having weak adhesion to the base film 152 is peeled off from the base film 152, leading to the occurrence of a clearance between the crosslinked film 154A and the base film 152.
Next, as shown in FIG. 28, in succession to washing with an aqueous isopropanol solution, a washing step and a drying step are carried out in this order to peel off the non-crosslinked portion of the second resist layer 154 thereby forming a second patterned resist layer 154B consisting of the crosslinked film 154A. In this manner, a frame having a narrowed trench is formed by the first patterned resist layer 153A and the second patterned resist layer 154B. At this time, there is a clearance between the second patterned resist layer 154B and the base film 152.
Next, as shown in FIG. 29, plating is carried out using the base film 152 as a seed layer by using a frame consisting of the first patterned resist layer 153A and the second patterned resist layer 154B to form plating layers 155A and 155B. Here, the symbol 155A represents an object patterned plating layer formed in the trench, and the symbol 155B represents a plating layer formed in other portions.
When the above plating layer is formed, a plating solution enters the clearance between the second patterned resist layer 154B and the base film 152, which causes the clearance to be plated, too. Also, the plating layer grows while it intends to spread and therefore the clearance is forcedly extended. As a result, the width of the bottom of the patterned plating layer 155A becomes greater than a desired width by the width of the second patterned resist layer 154B.
Next, as shown in FIG. 30, the frame is removed using an organic solvent. Then, as shown in FIG. 31, the base film 152 at the portion where the frame existed is removed by dry etching such as ion milling and reactive ion etching, or by wet etching.
Next, as shown in FIG. 32, a patterned resist layer 156 is formed to cover the object patterned plating layer 155A.
Then, as shown in FIG. 33, the plating layer 155B and the base film 152 disposed underneath that are no longer necessary are removed by wet etching. Thereafter, the patterned resist layer 156 is removed using an organic solvent to obtain an object patterned plating layer 155C comprising the plating layer 155A. The patterned plating layer 155C thus obtained has a shape in which the bottom is wider.
As described above, when the patterned resist layer formed by the finely patterned resist layer-forming method of the related art is used, the crosslinked film 154A is peeled off from the base film 152 because of weak adhesion between the crosslinked film 154A and the base film 152 and the strain of the first patterned resist layer 153A caused by heat treatment. As a result, a clearance is formed between the second patterned resist layer 154B and the base film 152. Then, when a patterned plating layer is formed using this patterned resist layer as a frame, the clearance is plated resultantly plated, too. Therefore, when a patterned plating layer is formed using the patterned resist layer formed simply by the finely patterned resist layer-forming method, there is the problem that a finely patterned plating layer cannot be obtained. This problem becomes more significant as the thickness of the resist layer to be the frame is increased.
As shown in Published Unexamined Japanese Patent Applications Hei 10-73927 and Hei 11-204399, when a patterned resist layer formed by the finely patterned resist layer-forming method is used as a mask to perform dry etching such as reactive ion etching in usual semiconductor manufacturing technologies, slight peeling of the crosslinked film 154A from the base film 152 poses no problem. The above-mentioned problem was therefore unpredictable.
It is an object of the present invention to provide a method of frame plating which enables to form a plating layer patterned more finely than the dimension determined by an optical limit, and a method of forming a magnetic pole of a thin-film magnetic head which enables to form a magnetic pole finer than the dimension determined by an optical limit, using the above-mentioned method of frame plating.
A method of frame plating according to the invention comprises:
a step of forming a frame using a resist and a step of performing plating by using the frame to form a patterned plating layer;
the step of forming the frame including:
a step of forming a first patterned resist layer by using a first resist containing a material generating an acid; and
a step of forming a second patterned resist layer by coating the first patterned resist layer with a second resist capable of entering into a crosslinking reaction in the presence of an acid, generating an acid in the first patterned resist layer, forming a crosslinked film in a portion of the second resist near the boundary that touches the first patterned resist layer, and peeling off non-crosslinked portions of the second resist, wherein the frame is formed using the first patterned resist layer and the second patterned resist layer; and
the first resist comprises the following compounds (A) to (D):
(A) an organic solvent;
(B) a base resin comprising a high molecular compound shown in the following formula (1), the compound having a weight average molecular weight of 10000 to 25000 and a molecular weight distribution as narrow as 1.05 to 1.25;
(C) an acid generating agent; and
(D) an aromatic compound having a group given by the formula xe2x89xa1C xe2x80x94COOH in its molecule: 
In the above formula (1), R1 represents a hydrogen atom or a methyl group, R2 represents a group represented by the following formula (2), R3 represents an acid-unstabilizing group different from R2: 
In the above formula (2), R4 and R5 each independently represent a hydrogen atom or a straight chain or branched alkyl group having 1 to 6 carbon atoms, R6 represents a straight chain, branched or cyclic alkyl group having 1 to 10 carbon atoms, or R4 and R5, R4 and R6 or R5 and R6 may form a ring. In the case of forming a ring, R4, R5 and R6 each independently represent a straight chain or branched alkylene group having 1 to 6 carbon atoms. Each of x and y denotes 0 or a positive number, provided that x and y are not 0 at the same time. z denotes a positive number wherein the following relationships are established between x, y and z: 0xe2x89xa6x/(x+y+z)xe2x89xa60.5, 0xe2x89xa6y/(x+y+z)xe2x89xa60.5 and 0.4xe2x89xa6z/(x+y+z)xe2x89xa60.9.
In the method of frame plating according to the invention, R3 in the formula (1) may be xe2x80x94CO2C(CH3)3.
According to the method of frame plating of the invention, it is possible to form a fine frame free from disorders during plating in the step of forming the frame, and it is therefore possible to form a fine patterned plating layer using this frame.
A first method of forming a magnetic pole of a thin-film magnetic head according to the invention is provided forming a layer including a magnetic pole portion of a thin-film magnetic head that comprises: a medium facing surface that faces toward a recording medium; a first magnetic layer and a second magnetic layer magnetically coupled to each other and including magnetic pole portions opposed to each other and placed in regions of the magnetic layers on a side of the medium facing surface, each of the magnetic layers including at least one layer; a gap layer provided between the magnetic pole portions of the first and second magnetic layers; and a thin-film coil at least a part of which is placed between the first and second magnetic layers, the at least part of the coil being insulated from the first and second magnetic layers. The layer including the magnetic pole portion is formed using the method of frame plating according to the invention.
The first method of forming a magnetic pole of a thin-film magnetic head of the invention makes it possible to form a fine magnetic pole using the method of frame plating of the invention.
A second method of forming a magnetic pole of a thin-film magnetic head according to the invention is provided for forming a layer including a magnetic pole portion of a thin-film magnetic head that comprises: a medium facing surface that faces toward a recording medium; a first magnetic layer and a second magnetic layer magnetically coupled to each other and including magnetic pole portions opposed to each other and placed in regions of the magnetic layers on a side of the medium facing surface, each of the magnetic layers including at least one layer; a gap layer provided between the magnetic pole portions of the first and second magnetic layers; and a thin-film coil at least a part of which is placed between the first and second magnetic layers, the at least part of the coil being insulated from the first and second magnetic layers, the method including the steps of: forming a layer to be patterned, the layer being to be the layer including the magnetic pole portion; forming a mask for etching on the layer to be patterned by the use of the method of frame plating of the invention; and forming the layer including the magnetic pole portion by patterning the layer to be patterned, through etching the layer by dry etching using the mask.
The second method of forming a magnetic pole of a thin-film magnetic head of the invention makes it possible to form a mask for fine etching by using the method of frame plating of the invention, and therefore makes it possible to form a fine magnetic pole by etching the layer to be patterned by using the mask.
Other objects, characteristics and advantages of the invention will appear more fully from the following description.